The present invention relates to a cross-groove type constant velocity joint used for propeller shaft or drive shaft of automobiles.
A cross-groove type constant velocity joint is such that each of guide groove of an outer joint member and each of guide groove of an inner joint member corresponding to each other are slewed in the circumferential direction opposite to each other, and a torque transmitting ball is retained and controlled in a track portion at which the both guide grooves are crossed, whereby since play between the torque transmitting balls and guide grooves can be decreased, the joint has widely been utilized for propeller shafts or drive shafts of automobiles where such play is not permitted.
FIGS. 4(a) and 4(b) illustrates an outer joint member 11 of a cross-groove type constant velocity joint. As shown in FIG. 4(a), guide grooves 11a slewed with a cross angle .gamma. in one circumferential direction with respect to an axial line X and guide grooves 11a slewed with a cross angle .gamma. in the other circumferential direction are alternately formed in an inner peripheral surface 11b of the outer joint member 11, FIG. 4(b) is a view showing the guide groove 11a when seeing the same from the inner diametrical side. A groove bottom line L is slewed with the cross angle .gamma. in the circumferential direction. Dotted lines at both side wall surfaces of the guide groove 11a are contacting lines C between a torque transmitting ball and the guide groove 11a. The left and right contacting lines C are parallel to the groove bottom line L and equidistant therefrom. However, boundary lines N between the guide groove 11a and the inner peripheral surface 11b are not parallel to the groove bottom line L but have an appointed inclination.
FIGS. 5A, 5B and 5C are cross-sectional views each taken along the lines A--A, B--B, and C--C of the guide groove 11a in FIG. 4(b). The A--A cross section shown in FIG. 5A is a cross section in the direction orthogonal to the groove bottom line L of the guide groove 11a at the inner side end, the C--C cross section shown in FIG. 5C is a cross section in the direction orthogonal to the groove bottom line L of the guide groove 11a at the front side end, and the B--B cross section shown in FIG. 5B is a cross section in the direction orthogonal to the groove bottom line L of the guide groove 11a at the joint center position 0. L' shows the perpendicular line connecting the ball center position 0' to the groove bottom line L, .alpha. shows the contacting angle, and X' shows the position of the axial line X. As shown in the same figure, although the groove depth (the length of an arc from the groove bottom line L to the boundary line N) of the guide groove 11a is identical between left side region and right side region at the joint center position 0 (B--B cross-section), the difference of the groove depth between left side region and right side region is gradually increased from the joint center position 0 toward the groove end side, wherein the difference is the maximum at the groove end (A--A cross section, C--C cross section). Such a construction necessarily results from the guide groove 11a having a cross angle .gamma. with respect to the axial line X, and the construction is inherent in cross-groove type constant velocity joints.
Generally, the guide groove 11a of the outer joint member 11 described above is formed by grinding, etc. after forging. Conventionally, in these production processes, the guide groove 11a has been worked so as to secure accuracy at all regions thereof.
Although the groove depth of the guide groove 11a of the outer joint member 11 is different between the left side region and the right side region at positions apart from the joint center position 0, when the guide groove 11a is given torque by the torque transmitting ball, it is the shallow side of the guide groove 11a that there is a fear of the torque transmitting ball coming off from the guide groove 11a, and the performance and durability of joints are determined by the groove depth at a shallow portion. Therefore, it is necessary to secure a groove depth required in view of design of joint at a shallow side, as a result, an outside region D of a deep side (see the A--A cross section and C--C cross section in FIGS. 5A and 5C) will become a region which does not have any relation to the performance and durability of joints.
However, in the conventional joint, machining to secure accuracy has been carried out even at the above mentioned region D which does not relate to the performance and durability of the joint. Such machining can be said to be a so-called excessive quality machining. Furthermore, a cycle time of machining is increased since the above mentioned region D is machined, thereby causing the productivity thereof to be decreased.
Therefore, in order to achieve the above mentioned problem, the present applicant previously proposed a construction in which the groove depth of the guide groove of the outer joint member is identical between the left side region and the right side region taking the groove bottom line of the guide groove as a reference, and is regular at all regions in the lengthwise direction along the groove bottom line of the guide groove (Japanese patent application no. 216725 of 1993).
However, when this kind of constant velocity joint transmits a rotational power while taking an operating angle, the load acting on the guide groove is not uniform on all regions in the lengthwise direction, but is the largest at the central region (normal use region) including the joint center position and becomes gradually decreased from the central region toward both ends. Therefore, with the construction already proposed (Japanese patent application no. 216725 of 1993), since the groove depth is regular at all regions in the lengthwise direction, there may be a fear that the load capacity of the central region (normal use region) will become insufficient, depending upon the use conditions.